Mobile communication systems have experienced explosive growth, as an ever- increasing number of subscribers demand mobile communication services. To meet this demand, increased system capacity is necessary, and can be achieved in many ways. One way is to reduce the "cell" size (that is, the coverage area of an individual base station). However, this approach also results in frequencies being reused within a smaller area, thereby increasing interference and decreasing speech quality. While factors such as fading and noise can also reduce speech quality, interference is typically the dominating form of disturbance; therefore, methods to reduce the effects of interference are highly desirable to improve speech quality.
Interference typically manifests itself as discordant noise, and can be difficult to remove. There are generally two types of interference: co-channel interference and adjacent channel interference. Co-channel interference (interference between two or more channels which are assigned to the same frequency, as mentioned above) is typically the dominant type, and varies with frequency reuse distance. Adjacent channel interference is generally controlled more easily, as it can be reduced to an acceptable level through appropriate filtering of the received signal.
To improve speech quality, many conventional systems employ diversity schemes, in which communication signals are received at two or more input branches. The branches are combined according to one of a variety of diversity combining techniques. One known diversity algorithm uses equal-gain combining to reduce interference. Equal-gain combining is a co-phase combining technique in which a combined signal is generated as the sum of the instantaneous phase envelopes of the individual branches. While relatively simple, this technique does not adequately reduce the effects of co-channel interference.
It would be desirable to reduce the effects of co-channel interference in a communication system, particularly in a system employing antenna diversity.